I (like many other people here) have an old computer power supply laying around, so I just short the two pins on the ATX connector and use the 12V line on a molex connector to simulate getting 12V from a car battery.

I (like many other people here) have an old computer power supply laying around, so I just short the two pins on the ATX connector and use the 12V line on a molex connector to simulate getting 12V from a car battery.

A battery CHARGER like the one linked usually has a pulsing output; that works better for charging batteries. You want a constant output (more or less) instead of pulsing. You can use the charger but it is best if it is also connected to a battery for it to charge and then your battery will filter and smooth the output somewhat. Then you can run whatever off the battery while it is being charged, much like when your alternator is charging it. The simpler way like others have said on here is to use an old ATX supply or some other 12V regulated output supply.